A modular-like system of offshore structures for imparting flexibility to the offshore exploration and production and transportation industries so that exploration, production and development work can take place over a large range of marine depths and operational circumstances with one or more marine...http://www.google.es/patents/US3716993?utm_source=gb-gplus-sharePatente US3716993 - Modular offshore structures system

A modular-like system of offshore structures for imparting flexibility to the offshore exploration and production and transportation industries so that exploration, production and development work can take place over a large range of marine depths and operational circumstances with one or more marine vessels, a family of spacing-jack-and-coupling means for stabilizing the vessels and for coupling them thereto, and a family of supporting stationing structures or modules which are used for lending support to the stabilized vessel or to operational structures established by the vessel.

BACKGROUND OF THE INVENTION There is in the offshore drilling, production, and transportation industry a variety of structures for supporting men and machinery at stations offshore. The structures are similar in basic function, namely to support the men and machinery in accomplishing their assigned functions. Otherwise the structures are significantly different in that some are mobile while others are stationary; and some are founded on the marine floor while others float. The mobile structures are commonly called mobile rigs while the fixed ones are fixed platforms. These rigs and platforms are generally classified as either drill ships, semi-submersibles, submersibles, jackups, pile jackets, or one of a few other hybrid designs. Each is peculiarly designed and adapted for a fairly limited set of operational conditions. As a result, there is restrictive flexibility of use. For example, the fixed frame design, commonly known as the aforementioned pile jacket, is best suited for permanent stations in water of a few hundred feet or less. All other current types are mobile and more expensive as a result, and therefore they are well suited for exploration work, but not so well suited for long duration stationary production work. However, even production work is not truly permanent and reusability would be a significant consideration in the design of a rig for production purposes. Fixed platforms are seldom used in exploration work because the cost of building a new platform for each exploratory hole is almost prohibitive, except in shallow, protected waters. Thus fixed platforms are primarily production type structures.

In contrast to the permanent station characterizing the fixed frame design, the most mobile type of offshore platform is the drill ship with its appropriate stabilizing and stationing apparatus such as thrusters, anchors and winches. The ship certainly is not best suited for permanent stationing because it is particularly sensitive to wave action by reason of the wide surface area of structure exposed to the water, and the use of thrusters to maintain stationing for long periods of time, as would be necessary for production activities, is economically unfeasible because of fuel consumption and the necessarily continuous human monitoring which is required. Also, of course, the ship is vulnerable to storms and generally adverse conditions.

Intermediate the permanent station characterizing the fixed frame and the high mobility of the drill ship are the family of rigs known as jackups. The jackup rig has some of the advantages of both the fixed frame and the drill ship. It is analogous to the former in that it is supported on the marine floor, and therefore is quitestable and requires no continuous operation or monitoring to maintain position. And, when the legs are raised, it can be towed from place to place so as to thereby provide a degree of mobility analogous to the drill ship. The legs can, of course, be lowered to varying elevations so as to provide the jackup with an adaptability to a variety of depths.

The aforementioned submersibles are also an intermediate form of rig. The submersibles and also the semi-submersibles have good stability, each is suited to its depth, the semi-submersible to deep water, the submersible bottom-founded frame to shallow water. Both are more stable but less mobile than the drill ship. They cannot be moved in heavy weather without jeopardy to themselves, their crew, and the towing vessel; and indeed some have even been lost while being moved in calm waters.

It thus becomes evident without further elaboration that each of the various types of offshore drilling rigs commonly used is well suited only to a relatively narrow range of operation. As a result, a company or firm which chooses to operate offshore must elect the particular type of rig best suited for its contemplated initial endeavor and thereafter be committed to the limitations of that rig when it is used in subsequent drilling operations.

The limitations inherent in the state of the art are best illustrated by a brief examination of one of the more common types of mobile rig. The jackup rig, as previously noted, has certain of the advantageous characteristics of the pile jacket in that it is founded on the bottom in a stable way while the apparatus it carries is supported clear of the highest anticipated waves so that the whole is fairly stable semi-permanent, albeit expensive, station. Mobility is achieved by lowering it bo'uyant platform to the water, and raising the legs from the marine floor, so that the whole can then be floatably moved to another location. Although jackup rigs in general are adapted to a relatively wide range of operating depths, namely about 20 to perhaps 500 feet, any single jackup is adapted, as a practical matter, to a very limited subrange within this range. For example, if a jackup of the prior art were to be designed for work in the Gulf of Mexico in water of 200 foot depth, it certainly could not work in depths of 400 feet because its legs would not reach the bottom. Likewise, it could not work competitively, that is economically, in water depths of say feet because other less expensive jackup rigs would be available for that work. So, although in a physical sense jackup rigs can work in a wide range of depths, they cannot in an individual and in an economic sense encompass a very large range of usefulness.

Therefore, it might be concluded from the above brief discussion that the offshore operator is restricted to a fixed location rig which represents a substantial investment, or to a mobile rig which represents a very substantial investment but which is adapted only to a relatively narrow range of operational depths which may represent a certain class of locations.

SUMMARY OF THE INVENTION The present invention endeavors to broaden the flexibility in use for offshore mobile rigs and ancillary structures, and to allow a wider variety of choices than presently exist. This is accomplished not by a specific modification to a particular type of existing rig, but by presenting the concept of an entire new family of modular elements which are adapted to cooperate with one another in order to provide a plurality of alternative structures which enable the user to operate an offshore drilling platform in a much broader range of depths and environmental circumstances than is presently known in the art. Briefly, and more specifically, the present invention is directed to a modular system of offshore structures consisting of one or more marine vessels which are adapted to cooperate with a variety of supporting structures and which are cooperatively operable in varying manners by being coupled together by a spacing-jack-and-coupling-structure. In more elaborate embodiments, the supporting structure will be incorporated into the spacing-jack-andcoupling-structure, so that the whole may serve as a spacking-jack-and coupling-structure for another supporting structure. In varying circumstances a releasable connection means is also provided for releasing the yessel from the structure or the structure from the vessel. This aforesaid releasable connection means may take a variety of forms. In one form it may release the spacingjack-and-coupling-structure from the vessel and not from the support structure. More commonly it may release vthe spacing-jack-and-coupling-structure from the support structure and not from the vessel. Sometimes both are done, and sometimes multiple releasable structures are formed into a whole by multiple releasable connection means. As a consequence of the factors of releasability and modularity, there is provided a family of individually independent but cooperating elements that afford much greater flexibility in use than has been known before in the offshore structures art. Therefore, a particular feature and advantage of this invention is its disclosure of a mobile rig for offshore operations which may be designed for a given purpose, such as competitive economical drilling in shallow water, but due to its inherent structural modularity.

characteristics it is adaptable to many varying functional applications, including drilling at much greater depths.

Another feature and advantage of the invention resides in a plurality of modules for reversibly converting a floating rig to a fixedly founded rig.

Still another feature and advantage of the invention is the provision for a plurality of structural modules which may convert a jackup rig to a semi-submersible and subsequently to a drill ship.

Yet another feature and advantage of the invention is the provision for a means for raising vessels out of the water and lowering vessels into the water regardless of whether the weight of the vessels is supported by the marine floor or by bouyance of the water.

Still another feature and advantage of the invention resides in the means and method for coupling marine structures and vessels together in order to markedly enhance their operational value.

A still further feature and advantage of the invention resides in a modular family of structures which enables a manufacturer to fulfill the changing requirements of his customers by converting a given rig from a first functional design to another functional design.

These and numerous other features and advantages of the invention will become more readily apparent upon a careful reading of the following detailed description, claims, and drawings wherein like numerals denote like parts in the plurality of views and wherein:

FIG. 1 schematically represents and illustrates the principal modular components of the system and their relationship to another.

FIGS. 2-6 illustrate a jackup structure which does not necessarily contact the marine floor in the usual and conventional manner.

FIGS. 7-30 illustrate, in general, an operational sequence portraying the evolution of a vessel similar to that shown in FIG. 1 from the stage of a drill ship to a pile-supported jackup, then into a jackup much like those of the prior art, then into a modification employing a semi-submersible wave transparent bottle frame (FIGS. 28-30).

FIGS. 31-34 illustrate a modified structural station module for resistance to heavy lateral loading and which is adapted for obtaining lateral stability in uncertain, variable depths.

FIGS. 35-42 illustrate still additional means of obtaining lateral stability through use of the modular system while adapting to uncertain depths and hazardous waters.

FIGS. 43-51 illustrate a variety of leg systems, both tensile and compressive, and a variety of isolating couplings, all employed in a jackup semi-submersible of the modular type disclosed herein.

FIGS. 52-58 illustrate use of the modular system for construction purposes, for building large modular structures at sea; and illustrate rotatable leg means.

FIGS. 59-62 illustrate further application of tensile legs to mat type jackup structures of a modular system, the legless jackup.

FIGS. -71 illustrate the use of multiple vessels on individual structures of the modular system.

FIGS. 72-77 illustrate first of all a prior art approach in which a jackup operates independently of other structures; and in which there is subsequently shown the modular system of the invention in which increased economy is produced without reduction in stability.

FIGS. 78-84 illustrate a further modification of the modular system concept in which a ring-like structure is utilized for supporting a jackup rig in medium depth water when a large number of wells are required for production.

FIGS. -90 illustrate a modification to the structure of FIGS. 78-84 for use in relatively deep water, this being accomplished by the rotatable leg means, similar to the sequence of FIGS. 52-58.

In my earlier filed application, Ser. No. 649,889, filed June 29, 1967, now U. S. Patent No. 3,575,005, there was disclosed a multi-purpose vessel and a multipurpose structure which through mutual cooperation permitted the vessel to navigably support the structure free of impediment and to alternatively allow the structure to stably support the vessel free of detrimental environment. There was also disclosed a method whereby the vessel could be navigated to an operating site in the water, founded and moved to another operating site, leaving behind at the prior operating site an operational platform which, in itself, could later serve as the means for founding a later arriving vessel. The present invention markedly enhances this prior disclosure by setting forth the means and methods by which a modular system of vessels, supporting structures, and releasable coupling means may be used interchangeably in the systems and methods not only set forth in said earlier